What is Remote I/O?

Remote I/O devices enable a level of flexibility and efficiency that is impossible to achieve using just local I/O. But what is remote I/O, and what is the best way to implement it? In this article we will answer these questions and more while we explore the numerous benefits of adding remote I/O to your control system.

Table of Contents

Introduction

In the context of an industrial control system, I/O (Input/Output) devices provide an interface that enables communication between field instruments and control devices. Field instruments may include things like sensors and actuators, while control devices typically refer to Programmable Logic Controllers (PLCs) or Industrial PCs. Put simply, I/O connections allow PLCs and other computers to receive input from sensors and send output to connected devices in the system.

Because of limitations that exist when transmitting a signal across long runs of wire, control system components and field instruments have traditionally needed to be installed in close proximity to each other. This “local” configuration reduces the chances of signal degradation or loss that can occur over long cable runs, but significantly reduces the range in which devices can be installed away from each other.

Fortunately there is another way. Remote I/O, or distributed I/O, refers to I/O devices that can be installed in a remote location away from the PLC, while still maintaining a reliable connection between it and the field devices in the system. Using remote I/O allows designers the freedom to place their equipment where it is most effective without worrying about reduced signal quality or expensive wiring requirements.

Local vs. Remote I/O

There are pros and cons to using either local or remote I/O, depending on the task at hand. In many cases a blend of the two will provide the best results, so it is important to understand how they compliment each other as part of a complete solution. Here is a quick breakdown showing some of the key differences between the two:

Local I/O

Local I/O refers to input and output devices that share a direct connection to the main controller within a short distance, usually within the same control cabinet or very close to it.

Characteristics:

  • Proximity: Devices are located near the main controller, limiting installation flexibility.
  • Wiring: Direct wiring to the controller can result in cluttered and complex wiring schemes, especially as systems grow.
  • Latency: Typically lower latency due to the short distance and direct connections, but modern networks mitigate this for remote I/O.
  • Reliability: High reliability with minimal signal degradation over short distances.
  • Maintenance: Easier to maintain in smaller systems since all devices are in a centralized area, but this can become cumbersome as systems scale.
  • Cost: Lower initial cost for smaller systems. These savings diminish as system size increases and wiring requirements become more complex.

Use Cases:

  • Small to medium-sized control systems where all components are in close proximity.
  • Applications where quick response times and minimal signal delay are critical.

Remote I/O

Remote I/O refers to input and output devices that are located away from the main controller and connected via communication networks or fieldbuses.

Characteristics:

  • Proximity: Devices can be located far from the main controller, offering increased flexibility across large or complex facilities.
  • Wiring: Uses network cables or fieldbus systems to connect remote I/O modules to the main controller, significantly reducing the amount of wiring required over long distances and simplifying overall system layout.
  • Latency: Comparable to local I/O when using a modern communication network. Older networks may see some increased latency.
  • Reliability: Remote I/O systems are highly dependable when part of a robust network infrastructure. Enables designers to build in redundancy to prevent downtime during an emergent event.
  • Maintenance: Although more complex due to the distributed nature of devices and network diagnostics, the modularity of remote I/O allows for easier troubleshooting and expansion.
  • Cost: Provides maximum value for large or distributed systems by reducing the need for long cable runs and simplifying future expansions.

Use Cases:

  • Large industrial plants where devices are spread out over a wide area, making centralized wiring impractical.
  • Applications requiring modularity and scalability, allowing for easy expansion by adding more remote I/O modules.
  • Systems where reducing wiring complexity and improving installation flexibility are paramount.

To summarize, remote I/O offers significant advantages in terms of flexibility, scalability, and reduced wiring complexity, making it ideal for large, distributed systems. Local I/O may be practical for small, compact control systems, but its advantages diminish as system size and complexity increase.

By combining both approaches, system designers can optimize performance, cost, and maintenance efficiency based on their specific application needs.

How Remote I/O Works

Implementing remote I/O will require a dedicated communication port on the PLC. If a remote I/O port is not built into the PLC, a communication module may be added for this purpose when using an expandable PLC model.

In the image below we have an expandable PLC that we will use as an example. The PLC module on the left has a limited amount of local I/O built-in, allowing field devices to connect directly to these I/O points. When a project requires more local I/O, the local I/O expansion module shown in the center may be added to provide additional points.

Illustration of a modular PLC with local and remote I/O capabilities
Figure 1 – PLC with local I/O and communication modules

To enable the connection to a remote I/O device, the PLC will need a communication port dedicated to this task. In our example the communication module on the right connects to the PLC’s expansion port to enable communications between the PLC and remote devices such as other PLCs, HMIs, or in this case, remote I/O modules.

Now let’s take a look at how this might work in a complete control solution. The following diagram expands on our last example, illustrating how local and remote I/O modules connect to a PLC as part of a larger control system:

Diagram of local and remote I/O configurations
Figure 2 – Diagram of control system integrating local and remote I/O.

As you can see above, local I/O expansion modules connect directly to the PLC’s backplane or expansion port, connecting it to any nearby field instruments in the system.

The remote I/O modules in this example are in a location far away from the PLC, connecting to the communication module with a high-speed data cable. This configuration reduces the need for extensive cabling, particularly in large facilities where field devices are in multiple separate locations. Instead of running dozens of wires across the entire site, the communication module serves as a bridge, transferring all process data to the PLC through a single cable.

Communication Protocols

When remote I/O modules send data back to the PLC, they use a specific communication protocol to do so. The protocol you choose will largely depend on device support, so it is important to confirm that the controller and remote I/O devices support the same protocol.

Depending on your needs and existing equipment, one protocol may be better for a particular task than another. Here is an overview and comparison of common communication protocols used in remote I/O systems.

Ethernet Industrial Protocol Logo

Ethernet/IP (Ethernet Industrial Protocol) is a common communication protocol in industrial automation. It leverages standard Ethernet technology to provide high-speed, reliable communication between devices on the factory floor. Some key features and benefits of Ethernet/IP include:

  1. Speed and Bandwidth: Ethernet/IP offers high data transfer rates and can handle large amounts of data. These qualities make it ideal for applications requiring real-time control and monitoring.
  2. Scalability: Supports a wide range of devices and network sizes, allowing for easy expansion of the system as needed.
  3. Interoperability: Being based on Ethernet standards, Ethernet/IP is compatible with a broad range of devices from various manufacturers, ensuring flexibility in device selection and integration.
  4. Diagnostic and Monitoring Capabilities: Ethernet/IP provides advanced diagnostic tools and monitoring capabilities, enabling quick identification and resolution of network issues.
  5. Standardization: Follows widely accepted IEEE 802.3 standards, ensuring a robust and standardized communication framework.

To implement remote I/O using the Ethernet/IP protocol, you will need an Ethernet communication coupler such as the iR-ETN or iR-ETN40R. For more information on how to use remote I/O with Ethernet/IP, check out this helpful connection guide.

For a deeper look at how to connect remote I/O while using the EtherNet/IP protocol, please visit our How to Connect Remote IO to an Allen-Bradley PLC over EtherNet/IP page.

Modbus Logo

Modbus is one of the oldest and most widely used communication protocols in industrial automation. It is simple to implement and highly versatile. Key features and benefits of Modbus include:

  1. Simplicity: Modbus is straightforward to implement and understand, making it a popular choice for a wide range of applications.
  2. Compatibility: It is widely supported by many devices and manufacturers, ensuring broad compatibility and ease of integration.
  3. Flexibility: Modbus can operate over various physical layers, including serial (RS-232/RS-485) and Ethernet, allowing for flexibility in network design.
  4. Cost-Effectiveness: Due to its simplicity and wide adoption, Modbus solutions are often cost-effective to implement and maintain.

Communicating with remote I/O modules using the Modbus protocol requires an Ethernet communication coupler such as the iR-ETN or iR-ETN40R. For more information on how to perform Modbus mapping for remote I/O applications, please refer to the iR-ETN User Manual.

For a deeper look at how to connect your remote I/O devices while using the Modbus protocol, please visit our Connecting Remote IO to PLCs Over Modbus page.

CAN Bus Logo

CAN Bus (Controller Area Network) is a robust communication protocol that is common in automotive and industrial automation applications. Key features and benefits of CAN Bus include:

  1. Reliability: CAN Bus is highly reliable, with built-in error detection and fault confinement mechanisms, making it suitable for critical applications.
  2. Real-Time Performance: It offers deterministic communication with real-time capabilities, which is essential for applications requiring precise timing.
  3. Noise Immunity: CAN Bus operates well in electrically noisy environments, making it ideal for automotive and industrial settings.
  4. Efficient Use of Bandwidth: The protocol efficiently uses bandwidth, ensuring quick and efficient communication between devices.

Remote I/O communication using CAN Bus requires a communication coupler such as the iR-COP. For more information on how to set up remote I/O using CAN Bus and the iR-COP, check out this connection guide.

EtherCAT Logo

EtherCAT (Ethernet for Control Automation Technology) is a high-performance Ethernet-based communication protocol used in industrial automation. Key features and benefits of EtherCAT include:

  1. High-Speed Communication: EtherCAT provides extremely fast data transfer rates, making it ideal for applications requiring high-speed communication and low latency.
  2. Precise Synchronization: It offers precise synchronization capabilities, essential for applications like motion control where timing is critical.
  3. Scalability: EtherCAT supports a large number of devices on a single network, providing excellent scalability.
  4. Flexible Topology: It supports various network topologies, including line, star, and tree, offering flexibility in network design.
  5. Efficient Data Handling: EtherCAT efficiently handles data by processing it on-the-fly as it passes through each device, reducing communication delays.

To enable remote I/O communication using the EtherCAT protocol, a communication coupler such as the iR-ECAT will be required. For more information on how to connect to remote I/O using EtherCAT, please refer to the iR-ECAT User Manual for specs, configuration tips, and examples.

Profibus Logo

Profibus (Process Field Bus) is another prevalent communication protocol in industrial automation, particularly in process automation and factory automation applications. Key features of Profibus include:

  1. Robustness: Profibus is known for its robust and reliable communication, even in harsh environments with high levels of electrical noise.
  2. Deterministic Communication: Profibus provides deterministic data transmission, which is beneficial for time-critical applications.
  3. Simplified Wiring: Profibus uses a bus topology, which can simplify wiring and reduce installation costs compared to point-to-point connections.

Profibus may have additional limitations in terms of speed and bandwidth compared to Ethernet/IP. Integrating older Profibus setups with newer Ethernet-based systems may require additional gateways or converters.

Applications

Cost Savings

Using remote I/O can result in a control solution that is easier to organize, deploy, and maintain, contributing to significant cost savings over time. By minimizing the amount of physical wiring, installation times are shorter, and material costs are reduced, leading to lower upfront capital expenses.

Because remote I/O can centralize control and simplify system architecture, it also lowers the potential for errors during installation and maintenance, further reducing costs associated with troubleshooting and downtime. Over the long term, the modularity and scalability of remote I/O systems mean that modifications can be made with minimal disruption and without the need for extensive re-wiring.

Large Facilities

Remote I/O is an ideal solution for large facilities that require centralized control. Remote I/O greatly reduces the amount of cabling required between field devices and PLCs that are located far from each other. Using remote I/O also allows a centralized PLC to collect input from multiple disparate stations across a facility.

Hazardous Areas

Certain locations may be too hazardous for personnel to work in during operations, making maintenance and troubleshooting a real challenge. Using remote I/O, control devices like PLCs can be installed away from field instruments operating in dangerous areas. This means that workers will be able to easily access their PLCs and other components from a safe location without shutting down operations.

System Upgrades

Remote I/O can be added to almost any pre-existing system regardless of the control device manufacturer. Simply connect a communication module that supports the appropriate protocol to your controller, then connect your I/O device. This can make system upgrades easier by reducing compatibility concerns, allowing you to update your I/O without being locked into a proprietary ecosystem.

Resources

For more ideas on how you can use remote I/O in your next project, take a look at some of our related resources:

Tutorials

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